The person hiding in the mirror was Illuso from the Hitman Team. Fugo ends up being dragged into the mirror by Illuso's Stand, Mirrorman. Fugo then summons his own Stand, Purple Smoke. Despite Giorno wanting to find Fugo, Abbacchio decides to go look for the key, since that was their mission. However, once Abbacchio finds the key, he also gets dragged into the mirror world...
I'm not letting him have that key!
!لن أدعه يحصل على ذلك المفتاح
Ich lasse nicht zu,
dass er den Schlüssel bekommt!
¡No dejaré que se lleve la llave!
¡No dejaré que se lleve la llave!
Il n’aura pas cette clé !
Non lascerò che prenda la chiave!
Não vou deixá-lo pegar a chave!
Я не позволю украсть ключ!